1. Field of the Invention.
This invention is in the general field of degradative technology by the use of biofilms and, more particularly, in the area of biological treatment reactors containing biofilms supported on a gas permeable membrane.
2. Description of the Prior Art.
In the field of degradative technology, new applications of biofilms are continuing to be developed for selected and non-selective removal of pollutants from both wastewaters and ground waters. Depending upon the depths of the biofilms and relative concentrations of the various potential substrates in the bulk solution, concentrations of the electron donors and electron acceptors in the biofilm can vary over wide ranges, providing several distinct micro-environments or "layers" for growth of various groups of bacteria based upon the electron donor and electron acceptor pairs. These types may include, but are not limited to, aerobic heterotrophic respiration, anaerobic fermentation, nitrification and denitrification.
For the selection of a successful process to treat municipal and various industrial wastes, engineers typically have attempted to control the reactor concentrations of the electron donor or the electron acceptor, and the solids retention time. With the proper control, a process can include various combinations of aerobic heterotrophic oxidation, anaerobic fermentation. In engineering practice, the practice of combining several bacterial groups in a single reactor has resulted in several treatment systems using conventional suspended growth and biofilm reactors. This approach for complex waste often results in a series of separate reactors with associated piping, pumping and clarifiers. However, considerable savings of construction, operation, and maintenance costs may be possible by developing systems that include all bacteria capable of anaerobic fermentation, aerobic heterotrophic oxidation, nitrification and denitrification within a single reactor.
Applicants have previously designed a similar device using oxygen for the removal of nitrogen compounds. The present invention is directed toward a system using oxygen and additional gases.